Solar Plane Aims for New Record: 3 Months Aloft Without a Pilot or Fuel

In July 2008 QinetiQ's Zephyr unofficially set the record for the most time aloft by a solar-powered plane. Now, the company is trying again, hoping to break that record by a factor of 10. Here's how they hope to do it.

Any day now, five people will toss one of the world's most sophisticated remote-control planes into the air at the U.S. Army's proving ground in Yuma, Ariz. It's the latest incarnation of QinetiQ's Zephyr, a solar-powered, high-altitude unmanned machine that unofficially set the record for the most time aloft in July 2008. It flew for 3.5 days. Now, its creators hope to break that record with the latest design tweaks. Their end goal is to fly for three months. But for this new version's first test flight, Zephyr's crew is aiming for two weeks in the sky.

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The bulk of the Zephyr is ultralight carbon fiber, banks of lithium-sulphur batteries and wings papered with thin-film photovoltaic arrays. The new version has a longer wingspan—74 feet compared to 56 feet on the previous model—with 50 percent greater area overall and wings that are deeper at the fuselage than at the tips. The bigger frame and more batteries make the aircraft over 40 percent heavier—it weighs in at 115 pounds, compared to its former 66.

"The real challenge has been pushing every element of the technology, from the efficiency of the engines to the efficiency of the aerodynamics to make sure it stays aloft for a long time," says John Saltmarsh, the program director for Zephyr's trials in Yuma.

The Zephyr is solar-powered during the day, cruising above the clouds at 65,000 to 75,000 feet. At that altitude, the Zephyr would be above most air traffic and should be able to fly unimpeded for the full duration of the record attempt. If it can reach stints of three months, Saltmarsh says, the Zephyr would be more akin to a satellite than an airplane. "The launching and recovery is an insignificant portion of the flight time, so it requires a different way of thinking," Saltmarsh says.

The plane can carry a payload of up to 6 pounds, which is just enough for cameras or other surveillance or communications equipment. Because of the surveillance potential, the Pentagon is footing some of the bill for its development, but QinetiQ claims a right to other civilian uses.

As a de facto satellite, the plane could circle above a tract of land and deliver whatever its payload is capable of. For example, it could act as a communications relay in rural areas, bringing an instant broadband network. It could aid in disaster relief, ocean monitoring, weather research, oil pipeline revisions, flood management and urban mapping, Saltmarsh says.

Now, Saltmarsh and the Zephyr crew are "running around like headless chickens over in Yuma at the moment," preparing for the launch, he said. When that day comes, five people will throw it in the air, and a team of three will control it. Depending on the complexity of the mission, planes could require three people to operate just one, or one person alone could operate up to four.

To fly for three months, the Zephyr will need some improved battery technology. In theory, the plane could fly indefinitely, but there are two main obstacles that will shorten its flights: Diminishing returns from the batteries will eventually render them too weak for an entire night's flight, and the electrical components will take a beating from solar radiation and will degrade over time.